The Kinect Up Close: Modifications for Short-Range Depth Imaging.

Microsoft's Kinect contains a diverse set of sensors, most notably a depth camera based on PrimeSense's infrared structured light technology. With a proper calibration of its color and depth cameras, the Kinect can capture detailed color point clouds at up to 30 frames per second. This capability uniquely positions the Kinect for use in fields such as robotics, natural user interfaces, and three-dimensional mapping. Thus, techniques for efficiently calibrating the Kinect depth camera and altering its optical system to improve suitability for imaging smaller scenes at low-cost are presented. An application of these techniques to enhance close-range obstacle avoidance in Kinect-based robot navigation is also demonstrated. To perform depth calibration, a calibration rig and software were developed to automatically map to raw depth values to object depths. The calibration rig consisted of a traditional chessboard calibration target with easily locatable features in depth at its exterior corners. These depth features facilitated software extraction of corresponding object depths and raw depth values from paired color and depth images of the rig and thereby enabled automated capture of many thousand data points. Depth calibration produced the fits upon Burrus's and Magnenat's functional forms, respectively. Fit f B2 (r) had residuals with µ = −0.22958 mm and σ = 5.7170 mm, and fit f M2 (r) had residuals with µ = 0.065544 µm and σ = 5.5458 mm. To modify the Kinect's optics for improved short-range imaging, Nyko's Zoom adapter was used due to its simplicity and low-cost. Although effective at reducing the Kinect's minimum range, these optics introduced pronounced distortion in depth. A method based on capturing depth images of planar objects at various depths produced an empirical depth distortion model for correcting such distortion in software. After compensation for depth distortion, depth calibration yielded the fit f B3 (r) = 1 m/(−0.0041952r + 4.5380), which had residuals with µ = 0.19288 mm and σ = 11.845 mm. Together, the modified optics and the empirical depth undistortion procedure demonstrated the ability to improve the Kinect's resolution and decrease its minimum range by approximately 30%. The ability of modified optics to improve obstacle detection was investigated by examining Kinect-based robot navigation through an environment with an obstacle placed around a blind turn. In separate tests using either the unmodified or the modified Kinect optics, a robot's navigation system was given a waypoint around the blind turn after first demonstrating navigability of the empty …